The present invention relates to a hydraulic drill, more particularly a hydraulic rock drill, and relates more specifically to a self-adaptive servo control system for a hydraulic drill, such that the operation of the drill is automatically self-adjusted according to varying conditions encountered during a drilling operation.
In the course of a drilling operation in rocky ground, the material being drilled is often non-homogeneous, and layers of different hardness are often encountered, with the result that the drill bit penetration into the ground, under constant impact power and feed power, varies substantially according to the conditions encountered. This may cause the drill hole to become plugged and the drilling operation to stop. It is therefore common practice for a drill operator to observe the penetration of the drill bit into the ground and to manually control the impact and feed powers accordingly, which prevents a single operator from simultaneously managing the operation of several drill rigs.
It is known, as disclosed in French Pat. No. 2,129,276, for example, to connect the impact unit of a hydraulic drill in series with the drill rod rotating motor whereby, in the event of increase of the drill rod resistance to rotation the pressure drop across the rotation motor reduces the power of the impact unit in order to prevent the drill rod from seizing or stalling. However, when the drilling operation is started, and more particularly when the ground being drilled lacks homogenity, this arrangement operates in a manner exactly opposite to what would be desirable. As long as the drill bit is rotating freely or is engaged in soft ground, the impact power is at its maximum, although the impact power and feed power should both be low in order to feed the drill bit into the soft material with lower vernier feed.
The inconveniences and shortcomings of the prior art are overcome by the present invention which provides a hydraulic drill in which the operation of the three hydraulic circuits, namely the circuit controlling the operation of the impact unit, the circuit controlling the operation of the rotation motor, and the circuit controlling the operation of the feed motor, are made mutually dependent in such a manner that the operation of the drill is automatic for all practical purposes, and that a single operator is capable of supervising the simultaneous operation of several drill rigs.